A Study of the Prevalence, Origin, Insertion, and Innervation of the Gantzer muscle – A Variant Forearm Muscle

Abstract

Gantzer muscles are variant muscles found within the flexor compartment of the forearm, located between the intermediate and deep muscular layers. The Gantzer muscle typically arises from the flexor digitorum superficialis muscle (FDS) and inserts either into the flexor digitorum profundus (FDP) or the flexor pollicis longus (FPL) muscle. In this 2020 summer research study, a total of 76 forearms from 38 prosected cadaveric specimens were dissected to investigate the prevalence, origin, insertion, and innervation of Gantzer muscles, when present. In total, Gantzer muscles were present in 68.4% (26/38) of the whole body donors and 60.5% (46/76) of the limbs. Of the 26 donors who possessed a Gantzer muscle, 20 (76.9%) specimens were documented as having this variant forearm muscle bilaterally. In addition, of the 46 forearms that possessed a Gantzer muscle, two limbs (4.3%) contained two Gantzer muscles within the same forearm. Concerning the specimens where the origin, or proximal attachment, of this accessory muscle were still intact within these prosections, 95% (38/40) of Gantzer muscles originated from the flexor digitorum superficialis. When the insertion, or distal attachments was not damaged in these previously dissected forearms, 80% (36/45) of Gantzer muscles inserted into the flexor pollicis longus, with the remainder inserting into the flexor digitorum profundus. In addition, within the intact forearms, 83.9% (25/31) of Gantzer muscles received innervation from the anterior interosseous nerve, with the remainder being innervated by the median nerve directly. Clinically, the presence of the Gantzer muscle can result in various compressive injuries, including impingement of the ulnar, common, or anterior interosseous arteries and neuropathy of the median or anterior interosseous nerve. Moreover, this variant muscle, which is more likely present than absent, should be considered during treatment and surgical management, especially during differential diagnoses for compartment syndrome of the anterior forearm. While only the 2020 results are presented, this study represents a small portion of a multi-year, expanded assessment of the prevalence, origin, insertion, and innervation of the Gantzer muscle.